This invention relates to a semiconductor light-emitting display device, particularly, to a device sealed with resin for protection of the semiconductor light-emitting elements.
A conventional semiconductor light-emitting display device sealed with resin is constructed as shown in, for example, FIG. 1 appended hereto. It is seen that the display device comprises a light-emitting assembly 16 housed in a casing 10. A predetermined portion of one wall of the casing 10 is formed of a transparent material so as to constitute a display portion 14 and the casing 10 is open to the outside on the side opposite to said one wall so as to provide an opening 12. The light-emitting assembly 16 consists of a stem 18, a plurality of light-emitting diodes 20, i.e., semiconductor light-emitting elements, and a plurality of terminals 22 connected to the diodes 20. The stem 18 is somewhat smaller than the opening 12 because the stem is inserted into the casing 10 through the opening 12. As seen from the drawing, the light-emitting diodes 20 are mounted to one surface of the stem 18 and the terminals 22 to the opposite surface of the stem 18. Further, a reflector 24 serving to guide the light emitted from the diodes to the display portion 14 are provided between the stem 18 and the display portion 14.
It is important to note that the diode 20 tends to be damaged by moisture, waterdrops, gases, etc. In order to prevent the damage, a liquid resin 26, which is solidified later, is poured into the casing 10 through the opening 12. Naturally, the gap between the stem 18 and the casing 10 shown in FIG. 1 is filled with the resin 26 and sealed after solidification of the resin. It follows that the moisture, waterdrops, gases, etc. are prevented from entering the casing 10 and, thus, the light-emitting diodes 20 are not damaged.
However, the conventional device described above gives rise to a serious drawback. Specifically, the liquid resin filling the gap between the stem 18 and the casing 10 tends to flow into the casing 10 before gelation. The flow of resin is particularly serious at the four corners of the gap. In some cases, the resin flowing into the casing 10 reaches the display portion 14 as shown in FIG. 2, markedly impairing the appearance of the produced light-emitting display device. Naturally, the display device stained with resin must be discarded. Since about 1 to 10% of the produced devices are stained with resin, the conventional device is low in productivity.
The flow of resin may be prevented if the gap between the stem and the casing is made very small. However, if the gap is too small, it is difficult or impossible in some cases to insert the stem into the casing. It should also be noted that the stem 18 is produced by punching, with the result that the corner portions of the stem are unavoidably rounded to some extent. In contrast, the casing 10 is produced by molding and, thus, the corner portions of the casing are scarcely rounded. It follows that the gap in question is enlarged at the corner portions, leading to the flow of resin even if the size of the gap is optimum except the corner portions.
The flow of resin can certainly be prevented by adjusting the properties of the resin such as viscosity, thixotropic property and time of gelation. However, a resin very suitable for preventing the flow into the casing may fail to fill the gap satisfactorily, rendering it impossible to prevent the moisture, etc. from entering the casing.
It is also possible to employ a double casting method for preventing the flow of resin 26 into the casing 10. In the double casting method, a small amount of resin is injected into the peripheral portion of the stem 18. After the resin mentioned has been cured, another resin injecting operation is applied to the entire region of the gap between the stem 18 and the casing 10. Clearly, this method necessitates an additional resin injection step, leading to a longer manufacturing time and, thus, to a low productivity.